Recruited Sera after moving to Skyhold and she isn't present.
She isn't marked anywhere on all 3 floors of the map. I checked on a forum to ask where she typically stands and they said near the dungeons. I checked and she isn't there either.
Forum Discussion
I don't know if you've found her now but if someone else comes along with the same problem I may as well answer it. Sera is located in the second floor of the tavern. If you walk around the second floor you'll find her in a small room with drapes and cushions.
